The advantages of transmitting voice information over a packet or cell switched network has long been recognised. The relative low cost of utilising packet switched networks such as the internet in place of a circuit switched network has generated growing interest and many telecom operators now claim that packet switching surpasses circuit-switched voice transmission in terms of bandwidth usage in their networks. This is due in part to the increase in products that provide voice over IP functions. However, it is also becoming increasingly interesting for network operators to enable telephone calls originating in a standard circuit switched network to be routed at least in part via a packet switched network without altering the way in which a user utilises a telephone or other telephony equipment.
An example of such an arrangement is described in British patent application No. GB 2 331 197. In this known arrangement, a circuit switched trunk network is replaced by a packet switched IP network. This has the advantage of allowing the telecom operator to keep the cost of trunk calls down while still utilising the regular circuit switched systems.
However, as packet switched technology gains importance compared to circuit switching, there is a need to incorporate more of the advantages of packet switched functions into a telecommunications system. Yet, if telecom operators are to continue receiving returns on the substantial investment represented by a circuit switched infrastructure, there is similarly a need to retain as much as possible of the circuit switched system